Wood treatment



. ture.

Patented June 1943' No Drawing. Application October 6, 1941, I Serial No. 413,909

9 Claims. (Cl. 16'i- -=-38;5)

Thi invention relates to wood treatment and more particularly to an improved agent for treat lng'wood. I

As is known there is a real need for a cheap and eflfective material for treating wood to waterproof the wood and prevent itsdeterloration under service conditions. Many such agents have been proposed in the past, of which creosote or similar oily bodies is typical. This type ofmaterial is subjected to many disadvantages among which are a rather short period of effective life a due to the tendency of the impregnatedcreosote to leach out of the wood as well as to bleed-out under elevated temperatures.

As a result of considerable. experimentation it has been found that chromium trloxide solutions have a very marked and unexpected effect on wood. It has. been found, for example, that when an aqueous solution of chromium trioxide containing of the order of about 1% to about 8 of the salt is-applied to wood, marked chemical and/or physical changes occur which distinctly beneficiates the wood. The wood treated with such a solution acquires a dark stain and develops a distinct waterproofness. Such treated wood, furthermore, has a lower flammability than the untreated wood. The impregnations by the treating solution greatly diminishes the tendency of the wood to burn with the usual flame and reduces the typical form of burning to a slow charring. r

A particularly uniqu feature of the improved type of wood treatment is its effect .on green wood. It has been found as a matter of actual tests that when green wood is treated with a chromium oxide-containingsolution, the solution rapidly penetrates the wood and greatly diminishes checking, cracking or shrinking of'the wood during subsequent drying. While no specific rationale of this effect is proposed it would ap- When wood is treated as above described, the

treated surface acquires a type of oleaginous tex- This is evidenced when the treated wood is immersed in water. .When thu immersed and withdrawn it is observed thatthe adherent water tends to accumulate in droplets; the described treatment therefore appears to have a. definite =efiect on the interfacial tension between the wood A particularly chromium trioxide upon wood it was observed I that some type of definite reaction obtain as was evidenced bythe change and color-of the wood and the striking modification of the moisture resistance of the wood. It is believed'that the unique properties imparted to the wood'are the result of the formation of definite complexes of the salt with components of the wood and possibly with 'the ligneous constituents.

It is further found that cellulosic material such.

as wood, paper, hemp fibers and the like, may

concept in another form. It is found, for example, that improved wood treatins solutions may be produced by treating or leaching sawdust with hot chromium trioxide solutions of varying concentrations and preferably of from about 2 to 8% of chromium trioxlde. In producing this solution the sawdust is preferably agitated in contact with the hot salt solution and heated for a few hours.

It is found thata definite action ensues. The original red color of the' solution changes to a dark-brownand the solution foams. When the heat is, discontinued and'the mas allowed to cool an oleaglnous scum appears on the liquid surface. If now the solution is boiled and the surface scum disappears the solution becomes more turbid ormuddy and the sawdust tends to become sticky.

At this point it is advisable to add a fresh solution of the chromium salt in an amount at least sufllcient to make up for evaporation losses during boiling. The mass is again heated for a period of from about one-half to about two hours and the solution separated from the residual sawdust as'for example by filtration. The filtrate,

which is of a darkish brown color is a clear solution free from suspended particles] and isdirectly available as a wood treating agent.

The solution thu prepared forms an excellent wood treating agent and imparts to wood the novel characteristics described above, particularly greatly improved water resistance, and-lowered flammability. "In making up the novel solution it is found that the concentration of the chromium trioxide in the aqueous solution and the proportion of the solution to the sawdust are not critical. In preferred operations solutions of from about 3% to about 8% of chromium trioxide may. be employed with from about 5 to about 30 or more parts by weight of the sawdust to the weight of the salt.

The novel wood treating solutions thus prepared may be applied to the wood in any desired manner, i. e. by immersion, brushing or spraying. If desired the wood to be treated may beimpregnated with the solution by utilizing a closed vessel and establishing a high hydrostatic pressure on the solution. j

It is found that in addition to its other advantages the wood treated with the new preserving composition accepts paint and lacquer films or coatings most satisfactorily. The new compositions described herein are most satisfactory for the treatment of marine piling and similar units subjected to the action of salt water and marine organisms and appear to present a definite protective etl'ect against the latter.

It will be understood that in utilizing the novel wood preservative solutions they may be made up and marketed as an aqueous concentrate which is diluted to the required degree prior t'o actual: use. It will also be appreciated that, if desired, there may be incorporated in the treattug-solution any additional compatible com-' pounds -the specific eflect of which is desired in the ultimately treated cellulosic material. In operating under the invention the solutions employed may be derived as the extract liquor from or from a sawdust produced from a different type of wood.

While preferred embodiments of the invention f'have=been described it will be understood that these are given to explain the lmderlying prin- -ciples involved and not as limiting the useful scope oftthe'invention to the described illustrative examples.

I claim: 7

1. A method of treating wood to improveits resistance to water which comprises applying to the surface a treating agent consisting essentially Ofdissolved chromium trioxide.

2. A method of producing wood treating solution which comprises extracting ground wood 'with'a hot aqueous solution of chromium trioxide and-separating the extract from the solid wood residue.

.3. A method of producing a wood treating solution which comprises dissolving chromium trioxide in water, heating the solution in contact with sawdust and separating the aqueous extract from residual sawdust.

4. A method of producing a wood treating solution which comprises extracting sawdust with a hot aqueous solution of chromium trioxide for a" period of approximately two hours; adding a fresh solution vof chromium trioxide solution to the extract and separating the resulting solution from the residual sawdust.

5. A method of waterproofing and preserving wood which comprises applying to the wood a preserving solution derived by extracting saw a sawdust correspondingto the wood'to be treated dust with an aqueous solution of chromium trioxide.

6. A method of waterproofing and preserving woodwhich comprises applying to the wood 'a solution derived by extracting sawdust with a hot aqueous solution of chromium trioxide.

7. A method of treating wood to enhance itswater resistance which comprises applying there- 

